Antithymocyte globulin treatment of retrovirus-induced feline erythroid aplasia: in vivo and in vitro studies.

The Kawakami-Theilen strain of feline leukemia virus (FeLV-KT) was used experimentally to produce erythroid aplasia in cats. The in vivo effects of goat anti-feline-thymocyte globulin (ATG) on hematopoiesis were investigated in FeLV-negative normal and FeLV-positive anemic cats. Treatment was initiated in anemic cats between 4 and 6 weeks postinoculation (PI) when erythroid progenitors were reduced to 10% of normal levels. During the first 2 weeks of treatment, ATG significantly increased the numbers of erythroid precursors in bone marrow from 15 to 35% in anemic cats and from 28 to 43% in normal cats. ATG stimulated a twofold increase of CFU-E and a threefold increase of CFU-GM in normal cats between 2 and 4 weeks after initiation of treatment but had no effect on CFU-E or CFU-GM in anemic cats. The in vivo effects of ATG were transient despite weekly treatment. Cats treated with normal globulin were not significantly different from untreated anemic control cats. In vitro treatment of low density bone marrow mononuclear cells with ATG plus complement increased CFU-E and BFU-E of bone marrow from cats prior to inoculation but not from viremic cats. These results indicate that, although ATG stimulates erythropoiesis and granulopoiesis in normal cats, it does not reverse retrovirus-induced erythroid aplasia.